1. Field of the Invention
This invention relates to an optical head for use in a data recording/reproducing apparatus for recording/reproducing data with the use of an optical recording medium.
2. Description of the Related Art
A separate-type optical head is known, which comprises a stationary optical system and a movable optical system, so as to shorten the seek time of the head.
The stationary optical system has a semiconductor laser located in a holding member, a shaping prism, a beam splitter, etc. A laser beam emitted from the semiconductor laser passes an opening formed in the holding member, and is directed to a stand mirror provided in a movable carriage unit. The beam reflected from the stand mirror is converged onto an optical recording medium by means of an objective lens.
If the opening of the holding member is not completely sealed, dusts enter the holding member, thereby adversely affecting the optical components therein. Specifically, dusts attached to the laser-passing surface of an element may reduce the power of the laser beam and/or increase the level of a signal noise. To overcome these disadvantages, Jpn. Pat. Appln. Publication KOKAI No. 3-165338 discloses a technique for adhering an optical element to that portion of the inner surface of the holding member which is located around the opening thereof, thereby sealing the opening and preventing dusts from entering therethrough.
If the above technique is applied to an irregularly-shaped optical element which serves as a shaping prism and also as a beam splitter so as to compact the stationary optical system, the attaching portion of the optical element must be made very small, and hence it is very difficult to attach it to the stationary optical system with high accuracy. Further, since in this case, an adhesive is coated on the overall periphery of the attaching portion which surrounds the passage of a laser beam, it is possible that the adhesive extrudes into the passage.
Moreover, Jpn. Pat. Appln. Publication KOKAI No. 2-257432 discloses a separate-type optical head, which has a guide shaft for guiding a movable optical system in a radial direction of an optical disk, and an optical block containing a stationary optical system. The optical block is fixed in position relative to the guide shaft, thereby enabling a laser beam emitted from the stationary optical system, to correspond to the optical axis of the movable optical system. In short, this publication discloses a structure which enables the emission point of a laser source to correspond to the optical axis of the movable optical system.
In general, the emission light from a laser source is allowed to have an inclination error within a range of 2 degrees. However, the above-described conventional technique does not consider an inclination of light from the emission point, and hence it is necessary to correct it actually. This is because even if the emission point of the laser source is made to correspond to the optical axis of a collimator lens, the axis of light deviates from the axis of the collimator lens when the flux of light has an inclination.
Jpn. Pat. Appln. Publication KOKAI No. 3-80523 discloses a separate-type optical head, which has means for correcting a deviation of an optical axis. In this optical head, an optical axis adjusting member is provided between a laser source and a movable optical system such that the adjusting member can rotate about the optical axis of a laser flux. The adjusting member performs predetermined angular adjustment to correct the deviation of the optical axis. However, the employment of the adjusting member inevitably makes the above-described optical head complicated in structure and in adjusting operation.
In addition, Jpn. Pat. Appln. Publication KOKAI No. 3-254448 discloses an optical head, which employs a half mirror and a wedge prism having a total reflection film and a polarization film. In this optical head, a laser beam emitted from a laser source is separated into an approach beam and a return beam by means of the half mirror, and a polarized component is separated from the approach beam by means of the wedge prism. The beams separated by the half mirror and the wedge prism are detected by optical detectors, respectively. In this case, it is possible that a change in the characteristics of the wedge prism is caused by changes in ambient temperature and with lapse of time, with the result that a light beam enters the portion of each optical detector which is deviated from a target portion, and an offset generates in a servo signal from the optical detectors.